Mount Arapiles-Tooan State Park, VKFF-0765 & VK3/VW-022, 15th December 2016

On the 14th December 2016 we left home on our driving holiday to Sydney to see our son and his family for Christmas. This is the seventh such road trip and before that he lived in Perth. We made at least three visits to Western Australia to see him and they were all camping trips with added expeditions, always involving radio and often staying in and activating National Parks before the WWFF program was conceived. Many, but not all, contacts were pre-arranged.

Our first overnight was at Naracoorte and early the next day set out for Ballarat where we were visiting old friends from our University days in the 1960s. On the way we visited Mount Arapiles-Tooan State Park to activate the summit. I was not eligible for the one point on offer as I had activated Mount Arapiles in March. Here is a link to that activation, my second:https://vk5bje.com/2016/04/21/mount-arapiles-vk3vw-022-vkff-0765-11th-april-2016/

However, I was keen to secure sufficient contacts to qualify the Park for the WWFF program aiming for at least 44 contacts. I made 24 contacts with VK 1, 2, 3, 5 and 7 stations and, with those already in the bank, now have the 44 needed. Here is my log for the activation:

Date:15/Dec/2016 Summit:VK3/VW-022 (Mt Arapiles) Call Used:VK5BJE/3 Points: 0 Bonus: 0 Delete

Time   Call   Band   Mode   Notes
00:06z VK5FANA 7MHz SSB
00:10z VK2UH 7MHz SSB
00:13z VK3PF 7MHz SSB
00:14z VK2KYO 7MHz SSB
00:15z VK3RW 7MHz SSB Ray Benalla
00:17z VK2HHA 7MHz SSB
00:19z VK2IO 7MHz SSB
00:22z VK7LTD 7MHz SSB
00:23z VK1DI 7MHz SSB
00:26z VK7FAMP 7MHz SSB XYL VK7LTD
00:29z VK5GJ 7MHz SSB
00:37z VK5PL 7MHz SSB
00:39z VK5PAS 7MHz SSB
00:42z VK5ZK 7MHz SSB
00:44z VK2EXA/3 7MHz SSB
00:55z VK3KAI 7MHz SSB
01:01z VK3GP/M 7MHz SSB
01:12z VK5GP 7MHz SSB Glynn Murray Bridge
01:14z VK5NRG 7MHz SSB
01:18z VK5GI 7MHz SSB
01:18z VK5ZPG 7MHz SSB
01:18z VK3GV 7MHz SSB
01:18z VK5ZPG 7MHz SSB
01:19z VK3SQ 7MHz SSB
01:20z VK5FANA 7MHz SSB
01:25z VK2UH 7MHz SSB
01:26z VK1DA/2 7MHz SSB

I did set up my antenna for 80 metres, but the only way I could do this was with each leg at 90 degrees to the other. I could not get the VSWR down low enough to use it. One of the challenges of setting up a portable antenna (a dipole) for 80 metres is the space required and on Mount Arapiles this was a challenge. I have subsequently used the antenna in a more traditional layout and it works really well. See my forthcoming post from Greater Bendigo National Park.

I would like to thank all of those operators who, during the busy Christmas period, took time out to give me a call. I hope Santa brought you all a new radio!

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The impact of trees on radio propagation, 8th December 2016

The Impact of Trees on Radio Propagation

John Dawes VK5BJE/VK5PF

This paper came about because Paul, VK5PAS, was told by a European amateur, who in responding to a photograph of Paul’s portable station, suggested his antenna was too close to trees and that this would impact negatively on propagation. Paul asked me to write something on this topic for Out and About.

I should declare at the outset that I do not have formal qualifications in physics and simply hold an AOCP (1977).

However, I said I would tackle the topic as an amateur radio operator.

Trees belong to a class of organic objects which include shrubs and ground cover plants, such as native grasses, which might all have a potential impact on radio propagation. The factor of interest is absorption, but could include other factors such as directivity. If trees and other foliage absorb radio frequency energy (RF), is this a serious matter and likely to adversely affect a portable amateur radio station? Many objects are able to absorb RF, for example, people, cars, rocks, hills as well as foliage.

In my experiments on 23 cm with Brian, VK5BC, Brian noted that an increase in signal strength at his home station occurred if he turned his beam towards the local silos at Gawler. I know from Amateur Radio Magazine, that Justin (VK7TW) reported that amateurs in Hobart use Mount Wellington as a passive reflector for 23 cm transmissions around the city and environs. Those of you with two metres and 70 centimetres transmission capability in your vehicles will know that antenna placement is critical in determining the radiation pattern. Roof top centre-mounted antennas are more likely to result in a donut-shaped radiation pattern and perform better. You are also likely to have experienced ‘flutter’ on mobile VHF and UHF, as well as with FM broadcast transmissions caused by objects, including plants, in the propagation path.

When it comes to absorption of radio waves by foliage this has been researched for several decades (see Goraishi, Takada & Imai, 2013, ch 6).

More recently telephone companies have driven this research on the impact of foliage on their UHF and microwave transmissions because they want to know how foliage might change the radiation patterns from their phone towers, especially when foliage is suggested as a factor in persuading the local neighbourhood to accept a tower, as was the case recently at Bridgewater in the Adelaide Hills.

An internet search revealed a plethora of articles, some scientific, of absorption at UHF and microwave frequencies and many articles by amateurs about foliage and HF. The latter were more subjective and observational as one would expect from amateurs who do not have the resources available to research institutions, government and military.

When I later conducted a search using Google Scholar I found well over 100 refereed journal articles. A meta-analysis of these is beyond my capacity and time. So returning to observational approaches to understanding absorption has been the field of amateurs.  Carefully recorded observations can be useful. I know from my own experiments on 70 cm using ATV (AM), SSB and FM foliage has an impact on signals. Flutter noise and fluctuating signals resulted, especially when the foliage was wet (see Meng et al, 2009) and the impact on ATV was more noticeable because of the 7MHz wide channel. With digital television signals, at home if I walk through the signal from channel 44 the picture pixilates.

At the empirical level many of the reported experiments targeting the interaction of radio waves with vegetation in a spatial sense used directional antennas (beams). This is the simplest approach (see Ghoraishi et al, 2013). Their conclusion ‘is that the airy spaces in the vegetated area can have a crucial influence in directing the signal toward specific directions, to be re-directed by foliage with the line of sight towards the receiver”. Or, in my words, such a situation can have unintended consequences in terms of the target area for your signal.

What about foliage at HF frequencies?

Should we give up using trees as antenna supports for our stations in the field or at home? My answer is a strong NO! Experiments at HF are much more difficult to construct. There are simply too many variables to control, for example, the sun (the K and A indices, the solar flux, the time of the year and the season), antennas, structure, type, direction, the skill of the radio operator (the art of communication) and equipment. What we can say is that trees are small, relatively in terms of wavelength. Australian trees, especially eucalypts, are generally less dense than trees that grow in colder climates, Europe and North America for example. And our portable experiences would be poorer if we couldn’t find a magnificent shade tree to keep the sun away in an extended activation while the tree also supports one end of the antenna. My view is that the losses in miss-matched antennas, batteries with reduced voltage and lack of operator skill are more likely to impact on the success of your day out.

Just beware that some Australian eucalypts can drop branches, especially on a hot day after wind. So be careful!

References

Giles-Clark, Justin, VK7-News, Radio and Electronics Association of Southern Tasmania (REAST), Amateur Radio Magazine, October 2016, pp 62-63

Ghoraishi, Mia, Jun-ichi, Takada and Imai, Tetsuro, (2013), Radio Wave Propagation Through Vegetation, Chapter 6. Accessed 6th October 2016. http://dx.doi.org/10.5772/52571

 Meng, Y. S., Lee, Y. H. and Ng, B. C., 2009, STUDY OF PROPAGATION LOSS PREDICTION IN FOREST ENVIRONMENT, Progress in Electomagnetics Research, B, Vol 17, 117 – 133

This article first appeared in Out and About, Issue 26 December 2016